The present invention relates to a disk array subsystem, which has a storage device such as a hard disk drive (HDD) and a controller that controls storing of data for a storage area provided by the storage device, and, more specifically, to a technique for making a diagnosis on a memory device contained in the controller.
The disk array subsystem uses a memory board (memory unit) on which a number of memory devices are mounted in its controller. The memory board typically includes a cache unit. For example, the memory device includes a SDRAM (Synchronous DRAM). The cache unit contained in the controller serves as a main memory of the controller and stores processed data. In a normal access operation of the disk array subsystem, the cache unit in the controller executes a data input/output between a host unit communicably connected to the controller and a HDD, wherein the cache unit is used to temporarily store transfer data. For example, in the normal access, when the controller reads/writes data from/to the storage area in the HDD in accordance with a request from the host unit, an access is made to a memory device in the cache unit to store the read/write data, etc. Note that, in the technique for the disk array subsystem, the memory device of the memory unit provided in the controller and the storage device such as an HDD, which is connected to the controller and is an object of RAID control, are different from each other in role and performance demanded by them.
In order to realize improved performance of the disk array subsystem, enhancement of reliability of data to be stored in the memory device contained in the controller is strongly demanded. Therefore, it is requested to make diagnoses of, by some means, whether data in the memory device is normal without any failures and/or whether input/output signals to the memory device are stable, etc.
Meanwhile, when the disk array subsystems are shipped to factories, there are made tests of confirming normal operations by fluctuating temperatures and/or voltages of the subsystem. In particular, the cache unit is subjected to a margin test of confirming the normal operations by fluctuating a characteristic such as voltage within a range of operational specification.
Japan patent Laid-open No. 8-212145 discloses a memory diagnosis technique in which test data is retained and such data and test data read from memory are compared.